Inhalational smoke (IS)-induced acute lung injury (ISALI) is a common clinical problem in major burn victims, contributing to the US annual burn-related death rate of 2-3 per 100,000 population, one of the highest in the developed world. ISALI is characterized by severe airway obstruction, fibrinous airway casts and debris and alveolar fibrin deposition. Airway casts are an important cause of lung dysfunction, morbidity and poor outcomes. There is no effective pharmacotherapy for this problem at this time. We have published preliminary data that shows that nebulization of tissue plasminogen activator; tPA improves lung dysfunction in our ovine model of ISALI. We have also published that perfluorocarbons (PFCs) offer unique therapeutic advantages for ISALI as they are mechanoprotective and cytoprotective, support gas exchange, and are uniformly distributed in the lung. These agents are also well-tolerated in the injured lung. We will test the hypothesis that fibrinolytic therapy appropriately delivered to airways is effective in both prevention and reversal of lung damage in ISALI. Our objective is to select the most effective fibrinolytic delivey regimen for treatment of ISALI. We will determine if a more bioavailable fibrinolysin that generates relatively lower levels of fibrinolytic activity; single chain uroknase PA (scuPA), or tPA, delivered either by nebulization or as a PFC suspension most effectively reverses lung dysfunction in ISALI in sheep. tPA is exquisitely sensitive to the major PA inhibitor in airway fluids; plasminogen activator inhibitor-1 (PAI-1), which is markedly increased in airway fluids in ISALI. Our new recently published preliminary data show that scuPA remains bioavailable via formation of PAI-1 resistant complexes with a2macroglubulin in airway fluids. Additional new preliminary formulation data show that we can create stable suspensions of fibrinolysins in PFCs and can optimize nebulization of the fibrinolysins. Our Specific Aims are: 1) To optimize formulations of tPA or scuPA-based fibrinolytic therapy for airway delivery. 2) Determine whether nebulization of tPA or scuPA or PFC-suspensions of tPA or scuPA most effectively protects against lung injury associated with ISALI and 3) To determine whether optimized airway delivery of fibrinolysins reverses lung dysfunction in established ISALI. Our team, led by experts in PFC drug delivery, ISALI, ovine modeling, fibrinolysis, drug formulation and delivery if drugs to the airway will apply a range of state of the art techniques to complete the aims. This project will likely yield novel, clinically tractable, potentially paradigm shifting approaches to safely improve outcomes in ISALI.